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Dusty rethink Some potential planet discoveries could be in doubt after a new study has found gaps in debris discs around young stars may be the result of something else.

A report in the journal Nature, found interactions between heated gas and debris disc dust can produce similar ring patterns to those caused by unseen planets.

Dusty ring patterns found around some young stars, such as Formalhaut, were previously thought to be caused by the gravitational effects of undetected planets that shepherd the dust into rings.

But study lead author Dr Wladimir Lyra of NASA's Jet Propulsion Laboratory in Pasadena, California, says the presence of gas in debris discs has been largely ignored.

"When observers saw these patterns they even went to the extreme of using the shape of these patterns to constrain the properties of the planets that they don't see," says Lyra.

"They see something that they can't explain, and then they blame it on the gravity of something that they don't see."

"We've found another way to generate these patterns," says Lyra.

The discs contain left over material after planetary formation, similar to the Kuiper belt, which contains icy debris, comets and dwarf planets orbiting beyond Neptune in our solar system.

Radiation from a star slowly depletes the gas in the disk over tens of millions years. However, some gas remains and could be replenished by collisions within the disc and its interaction with the star's solar wind.

"[The disks] are gas poor, which is not the same as saying they are gas free," says Lyra.

"It has been assumed that the amount of gas was so small that it wouldn't matter too much, but we show that's not really the case."

Alternate answer

Computer modelling carried out by Lyra and co-author Marc Kuchner of NASA's Goddard Space Flight Center, found high energy photons from the star, cause the gas to heat up, changing the way it orbits in the disk, and pushing dust particles into clumps and narrow eccentric rings.

They showed that small amounts of gas were enough to change the dynamics of dust sufficiently to produce gaps in the rings without the need of planets.

"When you take into account the dynamical effect of this gas, then we see many of the patterns that the observations show, and that simply wasn't expected," says Lyra.

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